Time to treat the bleeding obstetric patient like the trauma patient and lower the dose of opioid

Abstract

The 7th National Audit Project (NAP7) confirmed haemorrhage as a leading cause of maternal cardiac arrest[1]. In this audit of cardiac arrest in patients under the care of an anaesthetist, nearly half of the obstetric cases involved a general anaesthetic, and anaesthetic care was judged to be a key factor in 68% of cases. The specific drugs used for induction of anaesthesia were not recorded [1]. We speculate that over-generous use of opioids may be implicated. In the hypovolaemic obstetric patient, it is important to minimise the haemodynamic effects of induction. Most anaesthetists are familiar with techniques that achieve smooth induction for patients with cardiac disease. During and after training, anaesthetists come across more opportunities to care for such patients compared with managing major trauma. This may explain why, anecdotally at least, they tend to opt for a ‘cardiac anaesthetic induction’ comprising high-dose opioids with a reduced dose of induction drug when providing anaesthesia to patients who are haemodynamically unstable [2].

Liberal use of opioids in a hypovolaemic patient may, however, worsen haemodynamic status. Due to a reduced volume of distribution and clearance, plasma concentrations of fentanyl during haemorrhage can double. Activation of the sympathetic nervous system maintains cardiac output in the face of hypovolaemia through an increase in heart rate and systemic vascular resistance [3]. Fentanyl, through its sympatholytic action, can obtund these mechanisms, exacerbating haemodynamic instability, especially at high doses. It is for this reason that rapid sequence induction in a patient with shock is undertaken using limited doses of opioids, e.g. 1 μg.kg^-1 of fentanyl [4]. Once effective volume resuscitation has been established and blood pressure has increased, fentanyl can be titrated in aliquots to dilate the microcirculation and restore tissue perfusion, as evidenced by a reduction in serum lactate and base deficit [5].

To promote haemodynamic stability, we suggest that the anaesthetic management of an obstetric patient with haemorrhage should be more akin to that of a patient with trauma and shock by judicious use of opioids and induction with drugs such as ketamine. A ‘cardiac anaesthetic’ should instead be reserved for those with cardiac pathology.